The present invention relates to a hermetic screw compressor used for refrigeration and air conditioning and, more particularly, to a hermetic screw compressor suitable for a high-capacity refrigerator.
Conventionally, there has been known a hermetic screw compressor in which a screw rotor shaft is connected to a driving motor shaft with a coupling and the screw rotor shaft is supported by a high-pressure side bearing and a low-pressure side bearing, in which oil having been used for the lubrication of the high-pressure side bearing is caused to directly flow into a through hole formed in the center of the screw rotor shaft, being discharged as it is, and after being used for the lubrication of the coupling, the oil is mixed with low-pressure gas and is sucked in a tooth space portion of male and female rotors. The screw compressor of this type has been described in JP-A-5-113184 specification.
In the above-described prior art, the oil fed to the bearing has a high pressure and high temperature, and after the bearing and the gear coupling have been lubricated, all the oil is discharged to a low-pressure gas suction side, so that sucked gas is overheated and expanded. Also, there is a fear that a refrigerant contained in the lubricating oil is gasified, and the normal sucked gas quantity decreases, so that the compression function decreases. Further, if the discharge quantity of oil supplied for sealing to prevent compressed gas from leaking from the a rotor dedendum shaft portion to the bearing side is large, a shortage of oil occurs, and the sealing effect decreases, so that the compression function decreases. Further, if the quantity of oil discharged to the suction side is large, the quantity of oil sucked to the tooth space portion of male and female rotors increases, so that the quantity of oil contained in discharged gas increases.
The present invention has been achieved to solve the above problems, and accordingly an object thereof is to prevent a decrease in capacity of a compressor, decrease the quantity of oil contained in discharged gas, and decrease the quantity of oil discharged to the outside of the compressor.
To solve the above problems, the present invention provides a screw compressor in which a screw rotor is supported by a low-pressure side bearing and a high-pressure side bearing in a rotor casing, and the screw rotor and a driving motor are connected to each other by a coupling, and a drain oil passage is provided to return oil having lubricated the high-pressure side bearing to the low-pressure gas suction side through a through hole formed in the center of the screw rotor, wherein a throttle mechanism is provided in the drain oil passage to inject the oil.
Thus, since oil is injected by the throttle mechanism in the drain oil passage, the quantity of oil returning to the low-pressure gas suction side decreases, the sealing effect of the screw rotor section is improved, and the leakage amount decreases. Also, since the injected oil swirls with the rotation of the screw rotor, the cooling of oil is promoted, the overheating and expansion of sucked gas caused by oil and the gasification of a refrigerant contained in lubricating oil are reduced, the quantity of discharged gas is larger than the quantity of sucked gas, that is, the volume efficiency can be enhanced, and the suction amount at the time of gas suction decreases, so that the quantity of oil contained in discharged gas (discharge quantity of oil) can be decreased.
Also, in the above-described screw compressor, a member formed with a minute circular hole at the inlet of the drain oil passage can preferably be attached as a throttle mechanism.
Further, in the above-described screw compressor, the oil inlet side of the through hole preferably has a diameter smaller than the diameter of the through hole.
Further, the present invention provides a screw compressor in which a screw rotor is supported by a low-pressure side bearing and a high-pressure side bearing in a rotor casing, and the screw rotor and a driving motor are connected to each other by a coupling, in which oil for lubrication and cooling is fed from an oil sump provided in a high-pressure portion in the rotor casing to the high-pressure side bearing through an oil passage, flows into a drain oil passage formed in the screw rotor, is injected by being throttled at the inlet of the drain oil passage, is swirled with the rotation of the screw rotor, and thereafter lubricates the coupling.
Also, in the above-described screw compressor, a member for injecting oil at the inlet of the drain oil passage can preferably be attached to the screw rotor.
Further, the present invention provides a screw compressor in which a screw rotor is supported by a low-pressure side bearing and a high-pressure side bearing in a rotor casing, and the screw rotor and a driving motor are connected to each other by a coupling, wherein the screw compressor comprises an oil sump communicating with a high-pressure portion in the rotor casing, an oil passage connecting the oil sump to the high-pressure side bearing, a drain oil passage formed in the screw rotor, and a minute circular hole formed at the inlet of the drain oil passage to inject oil.
Also, in the above-described screw compressor, the minute circular hole is formed in a member which can be attached to the screw rotor.
Further, the present invention provides a screw compressor in which a screw rotor is supported by a low-pressure side bearing and a high-pressure side bearing in a rotor casing, and the screw rotor and a driving motor are connected to each other by a coupling, wherein oil for lubrication and cooling is injected through a throttle mechanism formed in the screw rotor to cool the screw rotor.